The overall objectives of this project are to characterize in detail the interactions of some important hemeproteins with lipid hydroperoxides. Spectrophotometric techniques will be used to define the reaction kinetics and to detect reactive hemeprotein or substrate intermediates. The involvement of free radicals in these reactions will be probed by novel electron paramagnetic resonance (EPR) techniques. Heme degradation products resulting from these reactions will be identified by sensitive analytical techniques, employing radioisotope labeling and high pressure liquid chromatography (HPLC). The experimental results are expected to clarify the physiological role of lipid hydroperoxides in the degradation of heme in vivo and also as oxidants in reactions catalyzed by membrane-bound hemeproteins, such as mammalian cytochrome P-450. Hemeprotein-hydroperoxide systems which are found to support the hydroxylation and/or dealkylation of typical drug substrates of liver microsomal cytochrome P-450 will be investigated as potentially useful model systems for elucidating the mechanism and control of the enzymatic activity of this important and complex microsomal hemeprotein.